Not Applicable
Not Applicable
1.Field of the Invention
The present invention relates generally to bulk material feeders and, more particularly, to a divergent inlet that improves material flow from the supply downcomer to the horizontal conveyor of the feeder.
2. Discussion of Prior Art
Those ordinarily skilled in the art will appreciate that numerous processes involve conveying a mass or masses of solid particulate material (alternatively referred to as bulk material) along a path from one location to another. Moreover, the material flow path will often involve a transition from generally downward flow to substantially horizontal flow. For example, bulk material will commonly pass through a downcomer to a substantially horizontal conveyor, whereby the material is directed downwardly through the downcomer to the conveyor and then carried horizontally away from the downcomer by the conveyor. Such an arrangement is often designed to move the material along the path or, in some instances, control the volume-rate or mass-rate of flow of material along the path. In addition, the downcomer and horizontal conveyor are often collectively referred to as a bulk material feeder.
In any case, there are often problems associated with material flow through a bulk material feeder. For example, the material is often not transferred to the conveyor at a uniform rate, even though there is a consistent rate of material being supplied to the downcomer. This problem has been particularly identified with respect to a certain type of bulk material feeder known as a gravimetric feeder. The gravimetric feeder includes a variable speed conveyor which may be designed to change speed in response to the amount of material being carried by the conveyor. In this respect, the conveyor speed may be increased or decreased to ensure that the desired amount of material is being moved by the conveyor. Manifestly, if the material is being unevenly transferred from the downcomer to the conveyor, the conveyor speed will necessarily have to adjust to accommodate for such fluctuations. The virtually continuous increase and decrease in conveyor speed presents numerous additional problems, including undue wear on the feeder components.
Those ordinarily skilled in the art will further appreciate that the downcomer on a gravimetric feeder traditionally includes a downstream discharge opening through which material is permitted to pass as it is moved along the path by the conveyor. In addition, the structure defining the discharge opening is designed to control the amount of material being transferred by the conveyor so as to facilitate relatively even and consistent volumetric transfer of material from the downcomer to the conveyor. This design, of course, assumes that sufficient material is being continuously deposited on the conveyor to cause the material that is moved out of the downcomer by the conveyor to be leveled off as it passes through the discharge opening. However, as will be set forth in further detail below, it has been determined that the traditional downcomer design simply does not permit the discharge opening to operate in the desired manner.
Another type of feeder that is susceptible to some of the aforementioned problems is a volumetric feeder. Such a feeder relies heavily on uniform and accurate volumetric flow and, contrary to a gravimetric feeder, includes no means for adjusting the belt speed in response to fluctuations in the volumetric flow rate.
Responsive to these and other problems, an important object of the present invention is to improve material flow through bulk feeders. In this respect, it is also an important object of the present invention to provide a bulk material feeder having uniform material flow from the downcomer to the conveyor. Another important object of the present invention to improve upon the construction of conventional volumetric and gravimetric feeder designs. Particularly, it is an object of the present invention to provide a feeder that does not suffer from undesirable conveyor speed fluctuations caused by uneven material flow.
In accordance with these and other objects evident from the following description of the preferred embodiments, the present invention concerns a bulk material feeder having a conveyor that is operable to convey material along a substantially horizontal path. Of course, if the principles of the present invention are being used on a gravimetric feeder, the conveyor speed may be adjustable responsive to the amount of material being carried by the conveyor. The feeder further includes a downcomer presenting a lower edge adjacent the conveyor, with the downcomer being configured to deliver the material onto the conveyor in an upright column. Moreover, the downcomer includes an innermost downwardly divergent surface which is believed to significantly improve material flow through the downcomer and onto the conveyor. The present invention also concerns a feeder inlet design that presents the divergent surface and is configured to be installed within an existing downcomer for improving material flow within the feeder without requiring extensive modification to the feeder. In addition, the present invention concerns the method of retrofitting an existing feeder with the inlet design.
Again, it has been determined that the divergent surface ensures that material flow is uniform from the downcomerto the conveyor. Particularly, it is believed that the divergent surface prevents the material from clogging within the downcomer as it flows downwardly toward the conveyor. It is also believed that the innermost divergent surface ensures that the discharge opening operates in its intended manner; that is, the structure defining the discharge opening serves to control the amount of material being moved away from the material column by the conveyor. As previously indicated, this leveling action facilitates uniform volumetrically efficient material transfer by the conveyor. In addition, it is believed that uniform material transfer by the conveyor is further facilitated by the fact that the divergent innermost surface provides essentially only lateral support to the material within the downcomer, such that virtually the entire material column confined by the divergent surface is supported on the conveyor. It is particularly believed that this relatively significant, downwardly directed pressure within the downcomer further decreases material flow fluctuations within the feeder and ensures that the material conveyed by the conveyor has uniform density.
Those ordinarily skilled in the art will appreciate that conventional bulk material feeders simply do not provide the advantages afforded by the present invention. It has been determined that this is primarily attributable to the traditional downcomer construction. Particularly, the downcomer wall is traditionally straight (i.e., generally parallel to the longitudinal axis of the downcomer), and it is believed that this straight-walled construction is not conducive to solid particulate material being fed to the conveyor by gravity and then through the discharge opening by the conveyor. It has further been determined that the material tends to bridge across the interior of the straight-walled downcomer and thereby create stoppages of material flow or, at the very least, uneven material flow. This phenomenon referred to herein as xe2x80x9cbridgingxe2x80x9d is a result of the cohesive force of the material and the adhesive force between the material and the downcomer walls overcoming the gravitational influence on the material. Furthermore, it has been determined that material flow to the conveyor is typically uneven enough and insufficient in quantity to permit the discharge opening from operating in its intended manner. These problems become even more troublesome when dealing with a xe2x80x9cstickyxe2x80x9d material or material that becomes more cohesive as its moisture content increases (e.g., coal).
Other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the accompanying drawing figures.